Prognostic value of residual hypoventilation in mechanically ventilated neuromuscular patients: A 5 years follow-up study

Abstract

Background: Home mechanical ventilation (HMV) is used to treat hypoventilation, and its efficacy is mostly assessed by daytime blood gases and nocturnal oximetry (SpO2). Transcutaneous CO2 measure (TcCO2) has shown higher sensitivity than SpO2 to detect hypoventilation in neuromuscular diseases (NMD) patients. No data exists on the prognostic value of these techniques. Aims: We aimed to compare the prognostic value of SpO2 and TcCO2 in ventilated adult NMD patients. Methods: Capno-oximetries performed between 2009 and 2011 in ventilated adult NMD patients were analyzed retrospectively and classified as showing “hypoxemia”, “hypercapnia” or being “normal”. Patients on oxygen therapy were excluded. Time to first ICU admission or death was collected as outcome of interest. Results: 55 patients were analyzed (age 28 [IQR 25-36.5] years; 71% Duchenne muscular dystrophy; vital capacity 11.5 [7.25-27.25] % of predicted; 51% tracheostomy). Capno-oxymetry was normal in 67% of patients, showing hypoxemia in 15% and hypercapnia in 27%. 9% had both hypoxemia and hypercapnia. Over a median follow-up of 4 years, we observed 12 deaths and 21 ICU admissions. The diagnosis-adjusted hazard ratio (95%CI) for mortality or ICU admission was 2.93 (1.24-6.91, p=0.01) for hypercapnia and 2.31 (0.85-6.23, p=0.10) for hypoxemia, when compared to the group with normal capno-oxymetry. Conclusions: Residual hypoventilation, assessed by capno-oximetry, has a negative prognostic impact in adult ventilated NMD patients. Accordingly, we suggest that capno-oxymetry should be included in the assessment of HMV efficacy in NMD patients, since TcCO2 identifies more patients at risk than oximetry alone.